This invention relates generally to memory modules which may act as system memory, for example, in connection with computer systems.
Rambus Dynamic Random Access Memory (RDRAM) currently offers sustained transfer rates of around 1,000 Mbps compared to 200 Mbps for ordinary DRAM memories. RDRAM may be used, for example, as the main or system memory in computer systems.
The Rambus In-line Memory Module or RIMM is a plug-in memory module for computer main memories. The RIMM may comply with the standards for the dual in-line memory modules (DIMM) form factor, but may not be pin compatible with the DIMM standards. A RIMM may implement the direct Rambus channel high speed bus which may operate at, for example, 400 megahertz.
A RIMM for the desktop computer applications may use traditional printed circuit board (PCB) routing techniques. However, the small outline version of the RIMM for laptop (SO-RIMM), or portable computers is considerably smaller than the RIMM used for desktop computers. According to current specifications of Rambus, Inc., as an example only, the desktop RIMM is 7.22 square inches while the laptop or portable version is 2.79 square inches.
This reduction in real estate available on the RIMM for portable applications complicates the SO-RIMM design. One design complication arises from providing the necessary route length for impedance matching. In addition, a problem may arise with RIMM modules that use an edge connector which extends along one edge of the PCB forming the RIMM. The integrated circuit Rambus memory chips themselves may be distributed along the length of the RIMM PCB. Thus, the routes must extend from the edge connector and turn through a relatively narrow turning region between the memory chips and the edge connector so as to extend around the memory chips to communicate with those chips.
Since the various routes are desirably matched in length, for impedance reasons, the narrow turning region provides a design constraint in designing for portable computer applications.
Thus, there is a need for an improved way of designing memory modules for portable and other reduced board area applications.